The present invention relates to a method and apparatus for forming transfer images in which an image printed by a thermal head and an ink ribbon on a image-reception layer formed on a transfer film in contact with the surface of a transfer drum is transferred together with the image-reception layer by the heating and pressurizing of the heat roller to an image-transferred member to form an image and to a transfer drum used in the apparatus, and more particularly to a transfer image forming method and apparatus capable of improving the thermal efficiency of a thermal head for a transfer film over the surface of the transfer drum and the reproducibility of gradation in printing and to a transfer drum used in the apparatus.
In general, a transfer image forming apparatus is an image forming apparatus that forms an image using dye or pigment as coloring material on an image-transferred member through a heating process or a heating and pressurizing process. Among such image forming apparatuses, one is based on an indirect transferring method in which an image using dye or pigment as coloring material is temporarily formed by causing the thermal head to thermally transfer the ink layer of an ink ribbon on the image-reception layer formed in a peelable manner on the transfer film serving as an intermediate recording medium, and thereafter the transfer film is heated and pressed against the image-transferred member with the heat roller so that the transfer image formed on the image-reception layer may be transferred together with the image-reception layer to the image-transferred member.
In one transfer image forming apparatus of this type, a buffer mechanism for removing the difference between the distance in the direction of the circumference of the rotating heat roller and the moving distance of the image-transferred member has been provided in a transfer mechanism, as in the transfer image forming apparatus disclosed in Japanese Patent Application No. 6-318003.
In another transfer image forming apparatus, there has been provided a burr removing mechanism that removes burrs in such a manner that burrs or foil fringes are prevented from appearing outside the image-reception layer on the image-transferred member when the image-reception layer on the transfer film is peeled and transferred from the substrate layer to the image-transferred member in transferring the image-reception layer on which the transfer image of the transfer film has been printed to the image-transferred member by heating and pressurization. Use of the mechanism enables the image-reception layer to be transferred sharply.
In one known image forming method with a transfer image forming apparatus, for example, in a thermal transfer method using thermal sublimation dye, a thermal transfer ribbon where thermal sublimation dye is coated over a base film and an image-transferred member to serve as a recording medium are stacked one on top of the other. On the basis of the image data prepared, the thermal transfer ribbon or the image-transferred member is selectively heated by the thermal head, thereby transferring and forming the desired image on the image-transferred member.
Typical image-transferred members used in such a method are card-like image-transferred members and booklet-like image-transferred members. The card-like image-transferred members include driver's licenses, identification cards, credit cards, bank cards, cash cards, employee identification cards, student identification cards, member's cards, chip card, smart card, contactless IC card, and optical cards. The booklet-like image-transferred members include bankbooks, passports, and visas.
The thermal transfer recording method using sublimation dye has disadvantages in that there are not many materials (dyeable materials) that can be dyed with sublimation dye. For example, the method can be applied only to image-transferred members composed of limited materials, such as polyester resin, acrylic resin, nylon resin, or vinyl chloride resin.
In spite of a desire to use materials other than the aforementioned ones, what has been proposed as means for thermal sublimation transfer recording using sublimation dye is as follows. In the image print section using a sublimation dye transfer ribbon and a thermal head, an image is first printed onto a dyeable material layer (e.g., a dyeable resin layer or a dyeable adhesion layer) on a transfer film serving as an intermediate recording medium where the dyeable material layer is stacked on a base film (a first recording), as disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication 63-81093. Then, in the transfer section, the image on the dyeable material layer of the transfer film is heated and pressed together with the dyeable material layer against the image-transferred member by means of the pressure drum, thereby transferring the image onto the image-transferred member (a second recording).
As for the transfer film, an intermediate recording medium, serving as an important technical element in the indirect transfer method including the first recording and second recording, one example of the basic stacked structure is composed of a base film, such as polyethylene terephthalate, a protective layer with an image protecting function, an image-reception/adhesion layer having the function of receiving an image and the function of causing the image to adhere to an image-transferred member, and a peeling layer provided so as to peel off between the base film and the protective layer. The image is formed on the image-reception layer/adhesion layer. In the second recording, the image-reception layer/adhesion layer, together with the protective layer, is peeled from the base film and transferred onto the surface of the image-transferred member.
While the image-reception layer/adhesion layer has been included in the layer structure, an image-reception layer with no adhesion to the image-transferred member may be used, depending on the material used. In such a case, the image is formed on the image-reception layer and can be transferred or stuck by providing an adhesion layer made of adhesive material on the image-reception layer or the surface of the image-transferred member, by sticking a film made of adhesive material on the image-reception layer, or by heating and pressurizing the transfer film and the image-transferred member with a film made of adhesive material sandwiched between the surface of the image-transferred member and the image-reception layer.
In the second recording, the transfer film on which the image has been formed and the image-transferred member are aligned with each other and heated and pressurized, thereby causing the image together with the image-reception/adhesion layer and the protective layer to adhere to the image-transferred member. At that time, the transfer film and image-transferred member are separated in the apparatus, whereas the image-reception/adhesion layer and protective layer carrying the image on the transfer film in the heated and pressured area is separated at the peeling layer section from the base of the transfer film and transferred to the image-transferred member. The transfer area on the image-transferred member is generally set according to specifications, taking into account the security, durability, and design of the image-transferred member.
The aforementioned conventional transfer image forming apparatus has generally a transfer drum and prints images on the thin-film image-reception layer stacked on the transfer film in contact with the surface of the transfer drum by means of its thermal head and an ink ribbon. The characteristics of the surface of the transfer drum has a significant effect on the reproducibility of gradation of the transfer image printed by the thermal head on the transfer film.